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After losing count of the number of sites that use the browser to shrink massive images into the size of the thumbnails that the page needs (and waiting forever for these large images to load), it is time to say enough.

The most common use case people have for images is small thumbnails that are used as an image link to another page that has the full size image on it, or the page only has space for a small image and the original is too large to fit. Doing this with ImageMagick is easy, even if the original aspect ratio of the image was not right.

convert is the name of the ImageMagick tool, -thumbnail 200x100^ creates an image that is at least 200 pixels wide and 100 pixels tall while preserving the aspect ratio of the original picture. This means that the resulting thumbnail can be larger than 200x100, but the image will not be distorted. The second part of the command -gravity center -extent 200x100 specifies that the resulting image should only be 200x100 and that the image should be picked from the center of the image. The gravity option can also be any compass direction with NorthWest being the top right of the image.

Processing multiple images is trivially easy, just specify a set of images using a wildcard like *.jpg and then the resulting images will be written out to a numbered set of files using thumb-%d.jpg, giving filenames like thumb-1.jpg, thumb-2.jpg and so on.